Re: Optimizing pglz compressor

On Monday, July 01, 2013 1:36 PM Heikki Linnakangas wrote:
> On 26.06.2013 16:37, Amit Kapila wrote:
> > On Wednesday, June 26, 2013 2:15 AM Heikki Linnakangas wrote:
> >> Can you also try the attached patch, please? It's the same as
> before,
> >> but in this version, I didn't replace the prev and next pointers in
> >> PGLZ_HistEntry struct with int16s. That avoids some table lookups,
> at
> >> the expense of using more memory. It's closer to what we have
> without
> >> the patch, so maybe that helps on your system.
> >
> > Yes it helped a lot on my system.
>
> Ok, good. Strange, I did not expect such a big difference.
>
> > There was minor problem in you patch, in one of experiments it
> crashed.
> > Fix is not to access 0th history entry in function pglz_find_match(),
> > modified patch is attached.
>
> Thanks, good catch! I thought that a pointer to the 0th entry would
> never make it into the prev/next fields, but it does. In fact, we never
> store a NULL there anymore, a pointer to the 0th entry is now always
> used to mean 'invalid'. I adjusted the patch to remove the NULL check,
> and only check for the 0th entry.
>
> Committed.

Thanks, will update the WAL Optimization patch based on this and post the
new patch and data on the corresponding thread.

With Regards,
Amit Kapila.